DESCRIPTION: The general goals of this project are to elucidate the central mechanisms underlying thermoreception and nociception. The specific aims of the proposed project are to determine the response properties of thermoreceptive neurons in the trigeminal brainstem complex and thalamus and their projection targets as well as to examine the interaction of thermoreceptive afferent inputs on the responses of nociceptive neurons. Electrophysiological extracellular single unitrecording techniques will be employed in anesthetized rats and cats. Recordings will concentrate on neurons located in the marginal layer of the medullary dorsal horn (MDH) although the possible existence of thermoreceptive neurons in deeper layers of the MDH and in trigeminal subnucleus interpolaris will also be examined. The responses of thermoreceptive neurons to innocuous and noxious cold and hot stimuli will be characterized. The projection targets of these neurons in thalamus will be determined by means of antidromic mapping techniques. The influence of descending influences from cortex and brainstem will be ascertained. Other experiments will examined the effects of skin cooling on the responses of nociceptive neurons in the MDH. In the second part of the project recordings will be made in thalamus of cats and rats and the responses and locations of thalamic thermoreceptive neurons characterized. These experiments will provide new data on the processing of temperature information in the trigeminal spinal tract nucleus and thalamus and clarify the mechanisms underlying cold pain. They will also examine the interactions of thermal cutaneous inputs with nociceptive inputs and may provide new insights on the central processing of nociceptive information.